Aeroelastic Load Simulations and Aerodynamic and Structural Modeling Effects

Transcription

1 SIMPACK Conference: Wind and Drivetrain Aeroelastic Load Simulations and Aerodynamic and Structural Modeling Effects Stefan Hauptmann Denis Matha Thomas Hecquet Hamburg, 17 June 2010

2 SIMPACK Conference: Wind and Drivetrain, 17 June Contents Dynamic Simulations in the WT Design Process Wind Turbine Modeling in SIMPACK Wind Turbine Aerodynamics in SIMPACK Blade element Momentum Theory (BEM) Non-linear Lifting Line Vortex Wake Model Computational Fluid Dynamics (CFD) Simulation Results Offshore Code Comparison Collaboration (OC3) Evaluation of Lifting Line Vortex Wake Model Validation of CFD Approach for Aeroelastic Simulations Offshore Applications Conclusions

3 SIMPACK Conference: Wind and Drivetrain, 17 June Dynamic simulations in the WT design process Wind Energy Specific standards and Guidelines Common Standards and Guidelines Site Wind Field Displacements Environmental Conditions Hydrodynamics Aerodynamics Guideline Loads Structural Dynamics Standards, Guidelines States of Operation Electr. System Dynamic Simulation of the System Wind Turbine Natural Frequencies and Damping Serviceability Analysis (geometry, resonance, dynamic stability) Control, Operation Structural Loads (time series or spectra, extreme values, load collectives) (Static) Mechan. Component model (FEM, analytical oder empirical) Ultimate Strength Analysis (fracture, buckling, fatigue) WT-Type Validation via Measurements [Fig.: R. Gasch, Windkraftanlagen]

4 SIMPACK Conference: Wind and Drivetrain, 17 June Integrated system model Major modules of a wind turbine simulation tool 1. wind field 2. rotor aerodynamics 3. structural dynamics including electro-mechanical system 4. control unit and actuators 5. Hydrodynamics (Offshore turbines) Offshore Wind Turbine Control Wind field Aerodynamics Rotor Electromech. System Dynamic interactions: major minor Wave field, currents, ice Hydrodynamics Support structure Grid (Tower & Foundation) Soil Soildynamics Environment Loads Support structure Consumption [Fig.: M. Kühn]

5 SIMPACK Conference: Wind and Drivetrain, 17 June Traditional dynamic model for aeroelastic simulation Model with 28 modal degrees of freedom (dof) Foundation: 6 dof s 3 translational (1, 2, 4) 3 rotational (3, 5, 6) Rotor blade (each): 4 dof s 2 flapwise (e.g. 16, 17) 2 edgewise (e.g. 18, 19) Wind R N 9, 10 K Tower: 5 dof s 2 fore-aft (7, 8) 2 lateral (9, 10) 1 torsional (11) 16, 17 18, 19 7, 8 y x z Additionals dof s: nacelle tilt (12) rotor rotation (13) main shaft bending (14, 15) drive train torsion (28) flexural beam F, T 2 3 [Fig.: Vestas]

6 SIMPACK Conference: Wind and Drivetrain, 17 June Motivation - Improvements needed Limitations of the traditional dynamic model Structure: Fixed number of only few modal degrees of Freedom Aerodynamics: Simplified representation of rotor aerodynamics by BEM theory Problem: Coupling effects are NOT considered Improvements for Structural dynamics Solution Flexible levels of detail for the wind turbine models More accurate models for rotor blades, drive train etc. Improvements for Aerodynamics Solution New engineering models for BEM? Codes, based on more advanced theories than BEM are needed to consider some aeroelastic effects Multibody simulation approach More sophisticated aerodynamic approaches

7 SIMPACK Conference: Wind and Drivetrain, 17 June Modular Integrated Simulation: SIMPACK - Wind Rotoraerodynamics BEM v 1 v 2 v 3 S SIMPACK Wind Turbine MBS Model Controller Interface Lifting Line-Method CFD Wind Field Generator, Converter Ständer P Ständer,, f Netz /// zum Netz AS-Läufer P Läufer ~ DC = = Filter ~ /// f Trafo Läufer [Fig. SWE, ECN, IAG, SIMPACK AG ]

8 SIMPACK Conference: Wind and Drivetrain, 17 June Dynamic wind turbine model in SIMPACK Traditional Dynamic Model Hub Drive Train FE-43 Bushing C14-Gearbox Gearratio (constraint) 28 Degrees of Freedom 0 DOF 0 DOF 0 DOF 0 DOF LSS_Hub 3 DOF,, Shaft torsion, bending LSS_Gearbox 1 DOF 1 DOF brake HSS FE-110 Proportional Actuator Cmp generator FE-165 Kinematic Measurement FE-143 Connector and Fct generators Pitch_ Reference_1 Pitch_ Reference_2 Pitch_ Reference_3 Drive train / base plate Used for a large number of load simulations (pitch) Blade_ Connect 1 (pitch) Blade_ Connect 2 (pitch) Blade_ Connect 3 0 DOF 0 DOF 0 DOF Tower, FE-13 Spring Rot 2 DOF yaw), (tilt) Bedplate_Connect 0 DOF Tower (Flexible Body) 4DOF Blades (Flexible Body) 4DOF/blade Foundation 0 DOF Foundation 6 DOF FE-43 Bushing x, y, z,,, Foundation_Ground UF22 Aerodyn 0 DOF

9 SIMPACK Conference: Wind and Drivetrain, 17 June Rotor Blade Models Automatic generation of 2 different kinds of rotor blade models Euler-Bernoulli or Timoshenko beam elements Modal Reduction Geometric stiffening Simple rotor blade Only bending modes are considered Sophisticated rotor blade Bending and Torsional Modes are considered Coupling effects are included

10 SIMPACK Conference: Wind and Drivetrain, 17 June The Control System Interface DLL interface Bladed compatible Baseline controller Variable speed below rated Collective pitch control above rated power El. power Rot. speed P rated Advanced control algorithms Individual pitch control (Tower-) Feedback controller Etc. Pitch angle [ o ] 90 o V in V rated V cut out Wind speed

11 SIMPACK Conference: Wind and Drivetrain, 17 June Generator Models (Variable Speed Generator) Static look-up table W gen Look-up table M geno Simulation of generator/converter system dynamics Control system M set FiFo PT2 PT1 W gen Losses Detailed electrical model of the coupled generator, converter and grid Ständer Electric system dead time P Ständer,, f Netz /// Low pass Drivetrain filter Converter delays P el zum Netz x Electrical & mechanical Losses (look-up table) + W gen Electrotechnical inertia PT1 M geno MatSIM AS-Läufer f Läufer ~ = DC = ~ /// Filter Trafo P Läufer Modeled in Matlab/SIMULINK Exported to SIMPACK Using MatSIM

12 SIMPACK Conference: Wind and Drivetrain, 17 June Blade Element Momentum Theory Basic approach: Load equilibrium in axial and radial direction Loads derived from the global momentum balance (depending on the induced velocities) = => Iterative derivation of induced velocities Important assumptions: 1. Stream Tube theory and splitting in isolated annuli (no radial interdependency) 2. No radial flow along the blades (problematic in combination with flow seperation and at the blade tip) 3. No tangential variation within the annuli (but empirical correction for finite number of blades) Loads at the local blade element (depending on the induced velocities)

13 SIMPACK Conference: Wind and Drivetrain, 17 June AeroDyn - Blade Element Momentum Theory Developed at the National Renewable Energy Laboratory, USA Empirical correction models: Tip-Loss Model: Prandtl Hub-Loss Model: Prandtl Turbulent wake state: Glauert Correction Dynamic stall model: Beddoes-Leishman Skewed Wake Correction: Pitt and Peters

14 SIMPACK Conference: Wind and Drivetrain, 17 June The OC3 Project The IEA Offshore Code Comparison Collaboration (OC3) is an international forum for OWT dynamics code verification Activities Objectives Discuss modeling strategies Develop suite of benchmark models & simulations Run simulations & process results Compare & discuss results Assess simulation accuracy & reliability Train new analysts how to run codes correctly Investigate capabilities of implemented theories Refine applied analysis methods Identify further R&D needs

15 SIMPACK Conference: Wind and Drivetrain, 17 June OC3 Participants & Codes 3Dfloat ADAMS-AeroDyn-HydroDyn ADAMS-AeroDyn-WaveLoads ADCoS-Offshore ADCoS-Offshore-ASAS ANSYS-WaveLoads BHawC Bladed Bladed Multibody DeepC FAST-AeroDyn-HydroDyn FAST-AeroDyn-NASTRAN FLEX5 FLEX5-Poseidon HAWC HAWC2 SESAM SIMPACK-AeroDyn Simo

16 SIMPACK Conference: Wind and Drivetrain, 17 June Exemplary SIMPACK/AeroDyn Result in OC ,0 NREL FAST (kn m) , , , ,0 GH Bladed (kn m) SWE FLEX5 (kn m) NREL ADAMS (kn m) Risoe HAWC2 (kn m) SWE SIMPACK (kn m) 20000,0 0,0 Model Results for Tower Base Bending Moment (OC3 Phase 1 DLC 3.2)

17 SIMPACK Conference: Wind and Drivetrain, 17 June AWSM Non-linear Lifting Line Vortex Wake Theory Developed at ECN, NL Blade representation: Lifting line [Fig.: ECN] Near Wake representation: Free surface of shed vortices

18 SIMPACK Conference: Wind and Drivetrain, 17 June Coupled Simulations: SIMPACK - AWSM Vorticity of rotor blade 1 t = 12s t = 6s t = 0s W Rotor Start-up procedure t Occurring wind gust Aeroelastic effects because of gust Simulation time: 12sec Mean Wind speed: 5 m/s Gust: 9m/s for 0.2 sec

19 SIMPACK Conference: Wind and Drivetrain, 17 June Demonstration Simulation Turbine: 1,5 MW NREL generic wind turbine 8 m/s wind speed Modeling approach Only the rotor (hub and three rotor blades) is modeled Flexible rotor blades Sophisticated model Coupling effects are considered Aerodynamics AWSM AeroDyn (with empirical correction models activated)

20 SIMPACK Conference: Wind and Drivetrain, 17 June Fast Individual Pitch Action Change of pitch angle for blade 1 (+7.3 for 10 seconds) Tip deflection blade 1 Tip deflection blade 3 Tip deflection blade 3 (detail view)

21 SIMPACK Conference: Wind and Drivetrain, 17 June FLOWer A RANS solver Developed to solve the three-dimensional, compressible, unsteady Euler or Reynolds averaged Navier-Stokes (RANS) equations Analyses the flow field around rotors (primarily for helicopters, adapted to wind turbines) Different turbulence models are available (but the k-ω SST turbulence model is the sole model used in this project) FLOWer features the Chimera technique allowing for arbitrary relative motion of aerodynamic bodies.

22 SIMPACK Conference: Wind and Drivetrain, 17 June Time-Accurate Fluid-Structure Coupling of Wind Rotors Loads calculation load projection on beam elements Loads on element nodes (principle of virtual disp.) FLOWer SIMPACK Grid deformation Conversion of deformations to quarter chord line Calculation of deformation Blade surface SIMPACK beam model Fluid Q n 2 Q n+1 Q n+2 Q n 1 Q n+1 Q n+2 t n t n+1 t n+2 Structure SIMPACK WEA model SIMPACK blade model with deformation

23 SIMPACK Conference: Wind and Drivetrain, 17 June Validation of Fluid-Structure Coupling Rotor moment [Nm] AeroDyn + SIMPACK FLOWer + SIMPACK Roto thrust [N] AeroDyn + SIMPACK FLOWer + SIMPACK Time-accurate aeroelastic simulation of the start-up phase (FLOWer + SIMPACK)

24 SIMPACK Conference: Wind and Drivetrain, 17 June Offshore Application I Adding capability of SIMPACK to model Offshore Wind Turbines (Floating & Monopile) Coupling of HydroDyn HydroDyn and SIMPACK Hydrodynamic Forces calculated with HydroDyn HydroDyn developed by NREL Participation in OC4 [Jonkman, NREL/TP ] SIMPACK

25 SIMPACK Conference: Wind and Drivetrain, 17 June Offshore Application II Mooring Lines are an important component for Floating WT Dynamics Currently mainly quasi static and linear models Introduction of a nonlinear multi-body mooring system model Improvement of load predictions by considering line dynamics, hydrodynamics, line-seabed interaction, nonlinear effects & anchor system Goal: Detailed modeling of floating WT in SIMPACK

26 SIMPACK Conference: Wind and Drivetrain, 17 June Conclusions The traditional approach for load simulations has limitations: The number of degrees of freedom for dynamic models is fixed The rotor aerodynamics is modeled using simplistic BEM theory SIMPACK offers advantages for load simulations MBS models with a variable level of detail can be generated Different aerodynamic modules can be coupled to SIMPACK to consider aeroelastic effects with the needed accuracy SIMPACK Interfaces to several aerodynamic codes have been developed AeroDyn (Blade Element Momentum Theory) AWSM (Non-linear Lifting Line Vortex Wake Theory) FLOWer (RANS solver)